Possible nova in M31
Tue, 2019-01-29 09:56
#1
Possible nova in M31
Nick James and I spotted this just after 6pm Monday 28th. The Liverpool telescope has it on their list but have bad weather and M31 is getting rather low in the sky for them. The nova is quite close to the core so may be a very difficult target for amateur spectroscopy. |
The BAA Journal |
|
© The British Astronomical Association 2019 |
|
Top banner image: |
Images
Nice find George/Nick !
I saw this pop up on my TNS alert yesterday but the skies had just clouded over. You are probably right though unless it brightens a bit. mag 17 is extremely marginal for me for a spectrum with enough resolution for a firm confirmation (ALPY 600) and as you say, the bright background wont help. It is on my list though. (I am starting to look at the potential to confirm M31 novae spectroscopically so if you like, you can contact me direct for a confirming spectrum if you find something interesting. The M31 season is probably closing for this now though as I need at least a couple of hours fully dark and at good altitude)
Cheers
Robin
There are at least four variable objects blinking on and off when I compare my median-subtracted frame from last night with one from early December. See if you can find them all here.
Some near the edge where the image overlap could be from a variety of causes.
I aligned the frames with Registar.
GIF too big for the forum, so loaded here: http://geoastro.co.uk/january2019/M31seq.gif
The arrows do make it much easier...
I make at least seven, most of which are quite faint. The pixel coordinates are close to (913,646), (708,707), (235,482), (274,843), (697,140), (939,483) and (562,850). This was only a casual inspection and there could well be more with a detailed search.
Hmm. Could be fun to write code to find these things.
You got more than me!
Yeah, the coding is fun. More fiddly, than difficult. I wrote some in VB6 a few years ago - that used Source Extractor output, but it could just as easily have used Pisa or Daophot instead. I imagine many would use Python instead of VB6 these days. :)
I'd use Perl myself but de gustibus non disputandum est. Further, I already have code to process Daophot and APT output and extending it to SExtractor shouldn't be difficult. My comment was more about the image processing end of things, to see whether a targeted approach optimised for just the one problem could be better (by some measure) than a general purpose tool.
Automation of detection of transients is one of the things that even pros struggled with for a long time but they seem to have got it pretty well sorted now. I remember back in the late 90s helping Tom Boles with this and the main problem was that you had to accept a pretty high false alarm rate in order to avoid missing stuff. At that time it was just more efficient to blink manually.
I've got a large C library of image processing functions written over the years. One of them takes two images at the same scale, cross correlates them in the frequency domain to get alignment, attempts to blur the sharper one to get the same median PSF as the other one, normalises and then subtracts. I have to say that it is not brilliantly effective and that in the end I decided that I had more interesting things to do!
The human eye/brain combination takes some beating.
On it now with the ALPY 600. It is there but barely above the background. Perhaps a hint of broad H alpha. Rain is due in 10 mins so an hours worth is all I am going to get tonight.
Very noisy at an SNR of just ~3-4. A blue continuum with no obvious features (though they would have to be very strong to show at this SNR) There is an emission feature at H alpha at the expected local velocity (-500km/s) but it could equally well be just noise.
Robin
Well done again George on another discovery.
Rob
Well done Robin - may be a few clear hours tonight from my location.
You are right about the M31 season drawing to a close.
My image quality goes to pieces around the middle of February.
Robin, Impressive spectra given how faint this is. The sky is still getting dark here but the nova is considerably brighter than the 28th. I get 16.7 R tonight compared to 18.0 R two days ago.
Yes indeed, much brighter.
I spent 2 more hours on the spectrum last night but no better. (The "light pollution" from the galaxy is just too much. The sky background in the slit is ~8x the star signal) so no spectroscopic confirmation yet I am afraid. If there is still no confirming pro spectrum I might try again in a few days when any characteristic spectral features should have developed more.
Robin
The spectrum has now developed sufficiently to attempt a classification.
It shows a clear broad (~1600km/s FWHM ) Ha alpha emission line and an H beta emission line at the expected radial velocity for this region of M31 so in the absence of any professional spectra, I have classified it as a Nova in TNS.
Robin
Excellent work Robin. Many thanks.
Superb work. Has this ever been done before - an amateur classification of an extra-galactic nova?
Hi George,
There is another one classified by me last October which was then also confirmed by professionals
https://britastro.org/node/15857
but I dont know of any others.
It would be nice to have a higher SNR spectrum to confirm the presence of other features (eg Fe curtain or He, N lines) but that would need a larger telescope. The spectroscopic evolution of an initial blue continuum with a strong H alpha emission emerging over time with around this velocity is characteristic of a nova though.
Cheers
Robin
Fascinating stuff, gentlemen! (not that I comprehend all the techicalities).
Well done indeed.
Hi Robin,
I tried to open the FITS file of the spectrum as on the TNS page - Maxim will not open it.
tns_2019agt_2019-02-04_18-35-15_Other_Other.fit
What am I doing wrong?
George
Hi George,
The fits file is 2 column data table (wavelength and flux) not an image so Maxim does not understand it. You can view the data in a free general fits data viewer like NASA's fv for example or alternatively download the dat file version and view it in notepad, excel etc. Better though is to view it in a free dedicated spectroscopy program like Visual Spec or ISIS etc. I have also loaded it into the BAA spectroscopy database so you can view it there too.
https://britastro.org/specdb/data_graph.php?obs_id=3607
Cheers
Robin
I learn something new every day!